Author: James Robertson
Date: 08:54:02 09/10/99
Go up one level in this thread
On September 10, 1999 at 09:41:17, Robert Hyatt wrote: >On September 10, 1999 at 02:34:09, James Robertson wrote: > >>On September 10, 1999 at 00:19:37, Robert Hyatt wrote: >> >>I store all my mates as bounds, a la Ferret (I think). My program solves the >>position in 1 second at ply 13 on my P233, 4MB hash table. (I used the EPD >>string from William's post). >> >> 1 -350 0 3 Kh3 >> 2 -370 0 16 Kh3 f2 >> 3 -365 0 51 Kh3 f2 Kg2 >> 4 -360 0 418 Kh2 Kf4 Kg1 Ke4 >> 5> -497 0 872 Kh3 Kf4 Kh2 Kg4 Kg1 Kxh4 >> 5 -497 50 872 Kh3 Kf4 Kh2 Kg4 Kg1 Kxh4 >> 6 -1169 50 1341 Kh3 f2 Kg2 Ke2 Kg3 f1=q >> 7 -1169 50 1894 Kh3 f2 Kg2 Ke2 Kh2 f1=q Kg3 >> 8 -1176 50 2636 Kh3 f2 Kg2 Ke2 Kh2 f1=q Kg3 Kd3 >> 9 -1246 50 3593 Kh3 f2 Kg2 Ke2 Kh2 f1=q Kg3 Qa1 Kf4 Qxa6 >>10 -1263 110 12151 Kh3 f2 Kg2 Ke2 Kh1 f1=q+ Kh2 Ke3 Kg3 Qxa6 >>11 -1326 220 25148 Kh3 f2 Kg2 Ke2 Kh3 f1=q+ Kg3 Qg1+ Kh3 Qg4+ Kh2 Qx >>h4+ >>12 -1331 380 63883 Kh3 f2 Kg2 Ke2 Kh3 f1=q+ Kg3 Qf3+ Kh2 Qg4 Kh1 Qxh >>4+ >>13 -29988 990 202497 Kh3 f2 Kg2 Ke2 Kh3 Kf3 Kh2 g5 hxg5 f1=q g6 Qg2+ >> >> >>I am surprised a 12 ply search does not see the mate; there might be a bug >>somewhere? >> > >Maybe... the move at ply=12 gives mate. If you go from there to your q-search, >and you don't recognize mates in your q-search, this might be perfectly normal. >In my case, when a regular search move gives check, I extend by one ply there. >In the PV I gave, the last move (at ply=12) is the only check, but it instantly >extends one ply, so that ply 13 is a full-width node and the mate gets picked >up. Otherwise it takes one extra ply, which is not important IMHO. IE do you >extend when you _give_ check or at the next ply when you detect you are in >check? Thanks for your answer; I think I found why my program does not see it. I recently revamped my extensions, and I _thought_ I had retained the "if we are in check but are going into the q-search, instead extend one ply". I guess I accidentally disabled it.... :\ At every other node it detects and extends when in check normally.... James > > > > >>James >> >>>Here is an interesting position given to me by Steffen Jakob: >>> >>> /p/P5p/7p/7P/4kpK/// w >>> >>> +---+---+---+---+---+---+---+---+ >>> 8 | | | | | | | | | >>> +---+---+---+---+---+---+---+---+ >>> 7 | *P| | | | | | | | >>> +---+---+---+---+---+---+---+---+ >>> 6 | P | | | | | | *P| | >>> +---+---+---+---+---+---+---+---+ >>> 5 | | | | | | | | *P| >>> +---+---+---+---+---+---+---+---+ >>> 4 | | | | | | | | P | >>> +---+---+---+---+---+---+---+---+ >>> 3 | | | | | *K| *P| K | | >>> +---+---+---+---+---+---+---+---+ >>> 2 | | | | | | | | | >>> +---+---+---+---+---+---+---+---+ >>> 1 | | | | | | | | | >>> +---+---+---+---+---+---+---+---+ >>> a b c d e f g h >>> >>> >>>Obviously black is getting crushed. He has one move, Kh3, which leads to a >>>mate in 6. Steffen asked me to try this and Crafty found a mate in 4, which >>>doesn't exist. I spent the entire day debugging this thing and here is what >>>I found: >>> >>>If you recall the discussion here a couple of weeks ago, I reported that I store >>>absolute mate scores (EXACT scores) in the hash table, and that I adjust them >>>so that they are always stored as "mate in N from the current position". This >>>has always worked flawlessly for me, and still does. >>> >>>For bounds, I once tried adjusting the bounds as well, but found quirks, and >>>left them alone. Wrong answer. To fix this mate in 4 problem, I decided to >>>adjust the bounds as well, but I now set any bound value that is larger than >>>MATE-300, by reducing it to exactly MATE-300, but still using the "LOWER" >>>flag to say that this is the lowest value this position could have. For bound >>>values < -MATE+300, I set them to exactly -MATE+300 and leave the flag as is. >>> >>>This position is cute. Because not only is it a mate in 6, but there are >>>transpositions that lead to mate in 7, mate in 8, and there are shorter (but >>>non-forced) mates in 4 and 5. And there are stalemates, and positions with >>>1 legal move, and so forth. >>> >>>You ought to find the following variation as one mate in 6: >>> >>>Kh3, f2, Kg2, Ke2, Kg3, f1=Q, Kh2, g5, hg, Kf3, g6, Qg2# >>> >>>If you find a shorter mate, it is wrong. If you find a longer mate, you >>>are probably just extending like mad on checks (crafty finds a mate in 8 at >>>shallow depths (9 plies, 2 secs on my PII/300 notebook), and doesn't find the >>>mate in 6 until depth 10, 3 seconds. >>> >>>It is a good test as the transpositions are real cute with white's king caught >>>in a tiny box, but with several different moves that triangulate and transpose >>>into other variations... >>> >>>If you get it right, you have either handled the bounds right, or else you are >>>very lucky. IE Crafty 16.17 gets this dead right. But if I disable the eval, >>>it goes bananas, yet the eval is not important when mate is possible. >>> >>>Have fun... >>> >>>I did... :)
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